This invention relates to a method of testing oil for ionic contaminants and for determining contamination of a refrigerant in a refrigeration system. More particularly this invention relates to a method of testing oil for ionic contaminants by measuring the conductance of water extracts of the oil. The invention is especially useful for testing the lubricating oil for a compressor drive of a refrigeration system of the type wherein there is contact between the refrigerant from the refrigeration system and the compressor drive lubricating oil. Testing this lubricating oil for ionic contaminants provides a method of testing the refrigerant for ionic contaminants because ionic contaminants present in the refrigerant also will be present in the lubricating oil due to the contact between the refrigerant and the oil.
Oil is used in a variety of applications such as a working fluid or as a lubricating fluid where the oil is within a closed system where it should be maintained in a relatively pure state to perform properly its intended function. Ionic contaminants in the oil indicate that the system is not functioning properly. Therefore, it is desirable to provide a method of testing oil for ionic contaminants.
The presence of ionic contaminants in the oil of a closed system may indicate a variety of problems depending on the type of system within which the oil is being used. For example, if the oil is being used as a hydraulic fluid then ionic contaminants in the oil may indicate a break-down of the oil. If the oil is being used solely as a lubricating fluid then ionic contaminants in the oil may indicate a physical break-down of the mechanical parts which are lubricated by the oil. Ionic contaminants in the lubricating oil for a compressor drive of a refrigeration system of the type having refrigerant from the refrigeration system in contact with the compressor drive lubricating oil, may indicate the presence of a water leak into the refrigerant of the refrigeration system. This is possible because excess water in refrigerant forms hydrogen chloride which is an ionic contaminant. This hydrogen chloride is found in the compressor drive lubricating oil because of the contact between the refrigerant of the refrigeration system and the compressor drive lubricating oil. Thus, testing this compressor lubricating oil for ionic contaminants can provide a quick, easy, inexpensive, and reliable method of detecting a water leak into the refrigerant of a refrigeration system, and the extent to which water has accumulated in the system.
Refrigerant in a typical refrigeration system can absorb a certain amount of water without substantially affecting the operation of the refrigeration system. Occasionally, some water may be present in the refrigerant due to moist air leaking into low pressure parts of the refrigeration system or due to small leaks in the heat exchanger tubing of the refrigeration system. The small leaks are caused by wear and tear of the tubing after prolonged use, corrosion of the tubing joints, and other such conditions. Typically, purging means are included as part of the refrigeration system to remove non-condensibles and water. However, when the amount of water introduced into the refrigerant exceeds the saturation level of the refrigerant then a more serious problem is posed to the refrigeration system. Excess water indicates that there may be a significant water leak in the refrigeration system. Excess water which cannot be absorbed by the refrigerant forms a water layer on liquid portions of the refrigerant in the refrigeration system resulting in the formation of hydrogen chloride. Hydrogen chloride is extremely reactive with materials, such as iron and copper, used in constructing a refrigeration system. Hydrogen chloride reacts with these materials to cause corrosion and deterioration of the materials.
Prior art methods of testing for water in refrigerant have included a colorimetric method and a hygroscopic salt method. According to the colorimetric method, refrigerant is circulated through a moisture sensitive indicator which changes color upon contact with moisture. The indicator senses excess water which cannot be absorbed by the refrigerant. According to the hygroscopic salt method, an electrode made of water absorbing salt is inserted in the refrigerant system so that when the electrode is in contact with water an electronic circuit is triggered which measures the conductance of the probe. Theoretically, the measured conductance is a direct indication of the amount of water in the refrigerant system.
These prior art methods of testing for water in refrigerant depend on where the sample of refrigerant to be tested is taken from the refrigeration system. Refrigerant is continually changing phase and moving through the refrigeration system whereby the water content of the refrigerant is not constant at all locations within the system. Also, since excess water floats on top of the liquid refrigerant at various places within the refrigeration system, any sample of refrigerant taken from a location, other than where this excess water is present, will give an indication of water content which is lower than the actual water content present in the system. Thus, choosing a sampling location is of critical importance when using these prior art methods of testing for water in refrigerant. In practice no sampling location can provide a representative sample of the refrigerant at all times. In the present invention a small portion of the refrigerant is constantly in contact with the compressor drive lubricating oil of the refrigeration system and deposits contaminants in this oil. Since the portion of refrigerant in contact with the oil is constantly changing, the amount of contaminants in the oil tends to be an average of the contaminants in the refrigerant of the refrigeration system.